When the bladder outlet is obstructed, the bladder muscle undergoes hypertrophy as a compensatory response to the increased resistance to urinary outflow. If the obstruction becomes chronic, bladder wall compliance decreases due to excessive hypertrophy and fibrosis. The poor compliance may lead to vesicoureteral reflux, hydronephrosis, and, ultimately, renal failure. Because of its clinical significance, we have begun to study the molecular control mechanisms that regulate the bladder hypertrophic response. One component of this response is the hyperplasia of the bladder smooth muscle cells (SMC). Using a model of the bladder wall in which bladder SMC are seeded in a collagen matrix and subject to varying degrees of resistance to contraction, the candidate has found that the cell cycle control protein p27KIP1 is downregulated by the development of increased tension within the SMC. Similarly, p27KIP1 was found downregulated in vivo in a murine bladder wall with bladder outlet obstruction. Then, using genetically manipulated mice, the candidate has found that the downregulation of p27KIP1 in response to stretch is necessary for bladder SMC hyperplasia during bladder outlet obstruction and that loss of p27KIP1 is sufficient to lower the threshold of the hyperplastic response of bladder SMC. The candidate has also determined that the upregulation of a second protein, Skp2 is necessary for both the downregulation of p27KIP1 and the bladder SMC hyperplastic response. Notably, whereas growth factors regulate Skp2 levels by altering the stability of Skp2 protein, we found that increased tension upregulates transcriptional expression of Skp2. The candidate would like to extend these studies with the guidance of Drs. Steven Weintraub and Douglas Dean who are experts of cell cycle control and transcriptional regulation. Specifically, the candidate plans to: 1) Identify the transcription factor(s) that mediates the increase in Skp2 promoter activity in response to increased tension in bladder smooth muscle; 2) Identify the mechanism(s) by which the transcription factor(s) identified in Specific Aim 1 is regulated by mechanical stretch of the bladder; 3) Examine the changes in phosphorylation of p27KIP1 threonine 187 and serine 10 that occur in response to changes in bladder wall tension. Through these studies, the candidate hopes to delineate the signal transduction pathways that regulate the bladder SMC hyperplastic response to bladder outlet obstruction in an attempt to find new targets for intervention to prevent the pathologic change in bladder compliance that occurs with either anatomic or functional bladder outlet obstruction. Work of this nature may decrease the morbidity and mortality that is caused by bladder outlet obstruction.